1. Field of the Invention
The present invention generally relates to a magnetoresistance effect element, a magnetic head and a magnetic reproducing system. More specifically, the invention relates to a magnetoresistance effect element for causing a sense current to flow in a direction perpendicular to the plane of the element to detect an external magnetic field, a magnetic head using the same, and a magnetic reproducing system using the same.
2. Description of Related Art
Conventionally, the readout of magnetic information recorded in a magnetic recording medium has been carried out by a method for relatively moving a reproducing magnetic head having a coil with respect to the recording medium to generate an electromagnetic induction to detect a voltage which is induced in the coil by the electromagnetic induction. On the other hand, an electromagnetic effect element (which will be hereinafter referred to as an “MR element”) has been developed. The electromagnetic effect element is being used for a magnetic sensor, and mounted on a magnetic head (which will be hereinafter referred to as an MR head) for use in a magnetic reproducing system, such as a hard disk drive.
In recent years, the size of a magnetic recording medium is decreasing, and the capacity thereof is increasing, so that the relative velocity of a reproducing magnetic head to the magnetic recording medium is decreasing during the readout of magnetic information. For that reason, it is required to provide an MR head capable of taking out a large output even if the relative velocity is small.
According to such a request, it has been reported that a multilayer film, such as Fe/Cr or Fe/Cu, wherein ferromagnetic metal films and magnetic metal films are alternately stacked on certain conditions, i.e., a so-called “artificial lattice film”, has a giant magnetoresistance effect (see Phys. Rev. Lett. 61 2474 (1988), Phys. Rev. Lett. 642304 (1990)). However, since magnetization is saturated in the artificial lattice film, a required magnetic field is high therein, so that the artificial lattice film is not suitable for the material of a film for an MR head.
On the other hand, there has been reported an example where a large magnetoresistance effect was realized even if a ferromagnetic layer is not antiferromagnetically connected in a multilayer film having a sandwich structure of ferromagnetic layer/non-magnetic layer/ferromagnetic layer. That is, a magnetic field due to exchange bias is applied to one of two ferromagnetic layers, which sandwich a non-magnetic layer therebetween, to fix magnetization, and the magnetization of the other ferromagnetic layer is inverted by an external magnetic field (a magnetic field due to signal or the like). Thus, by changing the relative angle between the magnetizing directions of the two ferromagnetic layers which sandwich the non-magnetic layer therebetween, a large magnetoresistance effect is obtained. A multilayer film of such a type is called a “spin-valve” (see Phys. Rev. B 45 806 (1992), J. Appl. Phys. 69 4774 (1981)). Since the spin-valve can saturate magnetization in a low magnetic field, the spin-valve is suitable for MR heads. However, since the rate of change in magnetic resistance of elements which have been already put to practical use is only about 20% at the maximum, it is required to improve the rate of change in magnetic resistance.
By the way, most of conventional MR elements have a type wherein a sense current is caused to flow in a direction parallel to the plane of an MR film constituting the MR element. This is called “CIP (current in plane)”. On the other hand, there is an MR element wherein a sense current is caused to flow in a direction perpendicular to the plane of an MR film. This is called “CPP (current perpendicular to plane)”. It has been reported that CPP can obtain a rate of change in magnetic resistance ten times as large as that of CIP (J. Phys. Condens. Matter. 11 5717 (1999)), and it is not impossible to obtain a rate of change of 100%.
However, if a sense current is caused to flow in a direction perpendicular to the plane of the MR film, there is a problem in that the electric resistance is very small, so that the output decreases. Therefore, it has been attempted to decrease the area itself of the MR film to raise the value of resistance to increase the output (Phys. Rev. Lett. 70 3343 (1993)). However, in the method for decreasing the area itself of the MR film, it is limited to cause the MR film to be a single magnetic domain.
In addition, if a sense current is caused to flow in a direction perpendicular to the plane of the MR film, an annular magnetic field due to current is generated in the plane of the MR film. This annular magnetic field causes to prevent a magnetization free layer, in which magnetization rotates with respect to the magnetic field due to signal, from being a single magnetic domain.
On the other hand, most of conventional MR heads have a “shielded” construction wherein an MR film is sandwiched between shields. In the case of the shielded construction, a floating magnetic field from a magnetic recording medium is directly detected by a spin-valve. However, in recent years, the recording density is further enhanced, so that a “yoke type” head for efficiently incorporating a magnetic flux from a magnetic recording medium into a magnetization free layer of a spin-valve via a magnetic flux guide (yoke) once has been proposed.
However, after the inventor's study, it was revealed that, in many magnetic heads represented by yoke type magnetic heads, it is required to define an active region, in which the detection of magnetism of an MR film is carried out, for various reasons.
As an example of this circumstance, a “planar type” head of yoke type heads will be described below.
FIG. 31 is a schematic perspective view showing the construction of a principal part of a planar type head. That is, the planar type head has a construction that a pair of flat yokes 20, 20 are arranged in parallel to the plane of a recording media 200. An MR film 100 constituting an MR element is provided so as to be magnetically coupled to the yokes 20, 20.
The recording medium 200 is provided with recording bits 200B along a recording track 200T. The magnetic flux due to signal from each of the recording bits 200B is supplied to a magnetic circuit, which is formed by the yoke 20, the MR film 100 and the yoke 20, to be detected. According to such a planar type construction, the length of a magnetic path to the MR film 100 is shortened, so that the magnetic flux can be efficiently led to a spin-valve (see IEEE Trans. Mag. 25, 3689 (1989)).
However, the width 20W of the yoke 20 of the planar type head is wider than the width 200W of the recording track 200T of the recording medium which has been acceleratively narrowed in recent years. For that reason, it is required to limit the active region of the MR film 100 for actually reading the magnetic flux.
In addition, in the planar type head, it is desired that the magnetic permeability is uniform and great so that the magnetic flux due to signal from the recording medium 200 efficiently enters the yoke 20 without being asymmetric and further enters the magnetization free layer of the MR film 100. Therefore, if a pair of magnetically hard materials 30, 30 are arranged so as to be perpendicular to the longitudinal directions of the track 200T of the medium so that the magnetization of the yoke 20 and the magnetization free layer is perpendicular to the track direction, the magnetic permeability can be high and uniform.
However, if a CPP type MR element for realizing a high magnetoresistance effect is used, it is required to provide an electrode portion (pillar electrode) for causing a sense current to flow through the MR film in a direction perpendicular thereto. If an annular magnetic field due to current from this electrode portion exceeds a magnetization fixing force due to the pair of magnetically hard materials 30, 30, the magnetization distribution of the magnetization free layer of the yoke 20 and the MR film 100 varies, so that the magnetic permeability is not uniform.
Moreover, if the CPP type MR element is used, the MR film 100 is sandwiched between top and bottom electrodes (not shown). Therefore, it was revealed that the magnetic field due to current from a portion of these electrodes parallel to the MR film 100 also influences the magnetization distribution in the yoke 20 and the magnetization free layer of the MR film 100.
The above described problems are not only caused in the planar type heads, but the problems are also commonly caused in most of yoke type heads or heads having other structures. For example, the same problems are caused in the “shielded” heads.